Mine Closure - Mining and the Environment: From Ore to Metal - page 825

With natural vegetation communities, reference to comparable local vegetation com-
munities is also important. However, it may be inappropriate and quite misleading to
compare the parameters in a 4-year old rehabilitation community with nearby natural veg-
etation that is at or close to its climax condition. More appropriate would be to compare
the rehabilitation community with natural vegetation at or about the same stage of suc-
cession. This may be possible, for example, in mountainous terrain where landslips occur
during the wet season in most years, but this will not always be practical. Also, it needs to
be recognized that colonization from adjacent areas will occur much more rapidly in a 1 ha
forest clearing than in the centre of a 50 ha rehabilitation area. There are many examples
in the literature in which the details of recolonization have been documented. An example is
the development of vegetation on Krakatoa Kecil, the new island that emerged following
the catastrophic Krakatoa explosion. However, again, there will be many cases where no
specii c quantitative data are available. In the absence of such information, the acceptance
criteria should be based on the identii cation of specii c occurrences that indicate that the
vegetation community is progressing according to plan. For example, monitoring should
seek to identify and quantify the following trends:
●

It may be inappropriate and
quite misleading to compare
the parameters in a 4-year
old rehabilitation community
with nearby natural vegetation
that is at or close to its climax
condition.

The occurrence of species other than those planted as part of the rehabilitation
prescription;

●

The suppression of cover crop species, if used;

●

Signs of successful reproduction, including l owering, seed set and germination;

●

Development of vegetation structure - i.e. different layers;

●

Appearance of seedlings of ultimate canopy species, and

●

Appearance of fauna, particularly insects such as ants and termites that are important
in recycling nutrients, while also attracting higher level predators.

Clearly, each situation is different, so that it is inappropriate to suggest a generic set of
acceptance criteria. However, for illustrative purposes, a hypothetical set of acceptance cri-
teria for rehabilitation of a min esite in the humid tropics could be:
●

No bare ground exposed in at least 85% of sampling sites, at end of wet season (access
tracks are excluded, coverage by leaf litter is included);

●

Progressive increases in l oristic diversity over at least four years;

●

Occurrence of at least 20 plant species other than those in initial cover crop;

●

Surface coverage by original cover crop species less than 5%;

●

Occurrence of a canopy involving at least four species;

●

At least 60% tree canopy cover (these need not necessarily be i nal canopy tree species);
and

●

Occurrence of at least two climax species as seedlings or saplings.

No Rehabilitation without Maintenance

It is rare for rehabilitation to be totally successful after a single preparation/planting pro-
gramme. This is particularly true of initial rehabilitation efforts. More commonly, supple-
mentary plantings and various maintenance treatments are required in order to achieve
acceptable groundcover in the early stages, and to ensure the development of appropriate
vegetation structure and diversity in later stages. Rehabilitation is at its most vulnerable
before, during or immediately following planting, germination and emergence ( Figure 21.7 ).
Heavy rain at such times can erode the seed bed soil, together with most of the seed, leav-
ing no choice but to repeat the programme. Mulch, jute netting and other temporary soil
covers can reduce but not eliminate the risk of such occurrences.

Rehabilitation is at its most
vulnerable before, during or
immediately following planting,
germination and emergence.